Photoluminescence of silicon nanocrystallites: an astrophysical application

Photoluminescence (PL measurements of size-selected silicon clusters thin f ilms generated by laser pyrolysis of SiH4 in a flow reactor and deposited a t low energy after a mechanical velocity selection are presented. Several p arameters have been investigated such as the mean size of the clusters. tin the range similar to 3-5 nm) and the dispersion of their size distribution . Particular attention has been paid to the determination of the absolute v alue of the PL efficiency. Measurements show that such silicon nanocrystall ites demonstrate high external PL efficiency (up to 12%) and strong depende nce of the PL properties on the cluster size. Results have been applied to the physical and chemical interpretation of spectroscopic observations in m any astronomical objects. of a broad. red emission band. This so called ext ended red emission (ERE) is attributed to the PL of an interstellar dust gr ain component when excited by the UV radiation emitted by a nearby star. He nce it has been shown that nanometer-size crystals of pure silicon are the best candidate materials as regard PL efficiency, peak wavelength and bandw idth. This demonstrates that size effects in interstellar grains play a dom inant role in the understanding of this astrophysical phenomenon. (C) 2000 Elsevier Science S.A. All rights reserved.